HALO.US is set to engage in a patent dispute with Merck (MRK.US) over the injectable version of Keytruda.

According to reports, HALO.US and Merck & Co. (MRK.US) are embroiled in a new patent dispute over the injectable version of Keytruda, Merck's blockbuster cancer drug.

HALO alleges that Merck has infringed on its patents and should have licensed them to sell the injectable Keytruda.

Merck's injectable version is based on an enzyme developed by South Korean company Alteogen, which is the company's solution to the upcoming patent cliff for its intravenous Keytruda. Keytruda accounts for nearly half of Merck's total revenue.

The Keytruda IV version will lose its exclusive rights in the U.S. market in 2028, when cheaper anti-PD-1 generics will come to market. Merck said last year that its injectable Keytruda met its primary endpoints in a key Phase 3 trial.

Merck also started a regulatory process last year to ask U.S. patent officials to reconsider some of HALO's patents for the Mdase enzyme because they are too broad.

HALO is reportedly to discuss the Keytruda patent issue at an investor event on Wednesday.

As of writing, Merck was down 0.54% before the market opened, while HALO was up 0.81%.